When a fluorescent compound absorbs ultraviolet light, for example, it may emit light in an optical band having longer wavelength than the ultraviolet light. The optical band of emission may take place as visible light, for instance.
Fluorescence may be applied in a plurality of fields such as measurements of chemical and/or biological fluid samples, for example. The samples may have natural fluorescence or fluorescent reagents may be added to the sample. A chemical and/or biological process may change the amount of fluorescent reagent or compound in the sample and hence by measuring the strength of fluorescence it is possible to determine the progress or quality of the process.
Fluorescence is usually measured by directing ultraviolet light to a sample and by receiving forward scattered fluorescent optical radiation typically in the visible band by a detector. The detector, which may comprise a dispersing element and photomultipliers in front of each detecting element, transforms the received spectrum of optical radiation into an electrical signal which may further be converted into a digital form. The digital spectrum may be analyzed and the concentration of the fluorescent compound in the sample determined by a computer with a suitable signal processing program.
However, both the measurement arrangement and the optical and electrical signal processing are complicated. Moreover, low cost detectors for measuring ultraviolet absorption and ultraviolet fluorescence are not available at the moment. Additionally, calibration of the fluorescence measurement is difficult which deteriorates the accuracy of the measurement. Hence, there is a need for a low cost and accurate device for measuring fluorescence.